1. Field of the Invention
This invention relates to, and has as its principal object, the provision of a novel device for measuring by acoustic means, the number and mass of individual particles borne in a fluid stream. Particular application of the invention is seen in the detection and characterization of particles in steam, especially superheated steam, water droplets in steam, dirt in an air stream, and particles in flue gases.
2. Prior Art
British Patent specification No. 1,435,972 teaches a device for detecting the presence of particulate material in a fluid stream flowing in a conduit. The device, which is directed to the detection of sand in crude oil and natural gas streams, comprises an acoustical detector disposed in the conduit. The detector, having a resonant frequency in excess of 100 kHz, produces an output signal corresponding to the vibratory energy produced by particle impact on the detector. The detector comprises a piezoelectric transducer confined in a cylindrical probe filled with oil. The probe is placed at right angles to the stream.
U.S. Pat. No. 4,149,415 teaches a device for distinguishing wheat grains from a mixture of straw and chaff. The device comprises a flat plate target disposed at right angles to the stream of particles in air. Attached to the downstream side of the plate are transducers inter alia which generate electrical signals corresponding to particle impacts on the plate. Resultant signals are electronically processed whereby to distinguish grain from straw and chaff. Spurious signals are suppressed electrically and transducers are mounted with opposite polarities whereby fundamental and odd harmonic modes cancel out.
The patent teaches against the use of a prior art cylindrical probe because the sensitivity varies across the width of the cylinder due to variation in the impact angle.